native xmake toolchain definition for UE-clang (#805)

This change is meant to provide a smoother experience when working on Linux. After this change, the toolchain setup process is now simply

```bash
$ scripts/ue_build_linux/get_ue_toolchain.sh 
```

and then at config time the toolchain is automatically detected if you downloaded it to the default location or have the `UE_TOOLCHAIN_DIR` environment variable set

```bash
xmake config --mode=debug
```

Compared to the old script-based approach this configures the toolchain more precisely, avoiding leakage into unrelated build processes such as when a package manager decides to build something like Ninja locally etc.

1 files changed, 1 insertions, 1 deletions

diff --git a/scripts/ue_build_linux/get_ue_toolchain.sh b/scripts/ue_build_linux/get_ue_toolchain.sh
index c2538b09a..0afd40fe3 100755
--- a/scripts/ue_build_linux/get_ue_toolchain.sh
+++ b/scripts/ue_build_linux/get_ue_toolchain.sh
@@ -5,7 +5,7 @@ ZEN_ROOT=$(realpath $SCRIPT_DIR/../..)
 
 die() { echo "ERROR: $1"; exit; }
 
-toolchain_dir="${1:-${ZEN_ROOT}/.tmp-ue-toolchain}"
+toolchain_dir="${1:-${UE_TOOLCHAIN_DIR:-${HOME}/.ue-toolchain}}"
 
 if [[ $toolchain_dir == "--help" ]]; then
 	echo "usage: $(basename ${BASH_SOURCE[0]}) <output_dir>"